sequences quiz

1) Im still having problems with identifying arithmetic and geometric sequences. I aslo get confused when in a problem they give you the second term and you use it as the first term to count how many jumps. Its also confusing finding a recursive definition for an arithemtic sequence like going step by step to find the final solution sometimes i get confused and dont know where to start.

2) The part i may struggle the most may be like organizing the steps to star solving the problem. what sould i do first in every problem?

3) The P.O.D problem is still difficult for me to understand as i said before in finding a recursive definition for arithemtic sequences:
the 4th and 20th terms of an arithmetic sequence are 3.5 and 4.8

a) find a recursive def. for the sequence

1) how many jumps?
2) total jump
3) size of one jump
4) t1?